First Dorsal Interosseous Muscle Research Articles

Changes in corticospinal excitability during motor imagery by physical practice of a force production task: Effect of the rate of force development during practice

Transcranial magnetic stimulation studies have indicated that the physical practice of a force production task increases corticospinal excitability during motor imagery (MI) of that task. However, it is unclear whether this practice-induced facilitation of corticospinal excitability during MI depends on a repeatedly practiced rate of force development (RFD). We aimed to investigate whether corticospinal excitability during MI of an isometric force production task is facilitated only when imagining the motor task with the same RFD as the physically practiced RFD. Furthermore, we aimed to examine whether corticospinal excitability during MI only occurs immediately after physical practice or is maintained. Twenty-eight right-handed young adults practiced isometric ramp force production using right index finger abduction. Half of the participants (high group) practiced the force production with high RFD, and the other half (low group) practiced the force production with low RFD. Questionnaire scores indicating MI ability were similar in the two groups. We examined the force error relative to the target force during the force production task without visual feedback, and motor evoked potential (MEP) amplitudes of the first dorsal interosseous (FDI) and abductor pollicis brevis (APB) muscles during the MI of the force production task under practiced and unpracticed RFD conditions before, immediately after, and 20 min after physical practice. Our results demonstrated that the force error in both RFD conditions significantly decreased immediately after physical practice, irrespective of the RFD condition practiced. In the high group, the MEP amplitude of the FDI muscle during MI in the high RFD condition significantly increased immediately after practice compared to that before, whereas the MEP amplitude 20 min after practice was not significantly different from that before practice. Conversely, the MEP amplitude during MI in the high RFD condition did not change significantly in the low group, and neither group had significant changes in MEP amplitude during MI in the low RFD condition. The facilitatory effect of corticospinal excitability during MI with high RFD observed only immediately after physical practice in the high RFD condition may reflect short-term functional changes in the primary motor cortex induced by physical practice.

Sex differences in laterality of motor unit firing behavior of the first dorsal interosseous muscle in strength-matched healthy young males and females

PurposeThe purpose of this study was to compare laterality in motor unit firing behavior between females and males.MethodsTwenty-seven subjects (14 females) were recruited for this study. The participants performed ramp up and hold isometric index finger abduction at 10, 30, and 60% of their maximum voluntary contraction (MVC). High-density surface electromyography (HD-sEMG) signals were recorded in the first dorsal interosseous (FDI) muscle and decomposed into individual motor unit (MU) firing behavior using a convolution blind source separation method.ResultsIn total, 769 MUs were detected (females, n = 318 and males, n = 451). Females had a significantly higher discharge rate than males at each relative torque level (10%: male dominant hand, 13.4 ± 2.7 pps vs. female dominant hand, 16.3 ± 3.4 pps; 30%: male dominant hand, 16.1 ± 3.9 pps vs. female dominant hand, 20.0 ± 5.0 pps; and 60%: male dominant hand, 19.3 ± 3.8 vs. female dominant hand, 25.3 ± 4.8 pps; p < 0.0001). The recruitment threshold was also significantly higher in females than in males at 30 and 60% MVC. Furthermore, males exhibited asymmetrical discharge rates at 30 and 60% MVC and recruitment thresholds at 30 and 60% MVC, whereas no asymmetry was observed in females.ConclusionIn the FDI muscle, compared to males, females exhibited different neuromuscular strategies with higher discharge rates and recruitment thresholds and no asymmetrical MU firing behavior. Notably, the findings that sex differences in neuromuscular activity also occur in healthy individuals provide important information for understanding the pathogenesis of various diseases.

Abnormal motor cortical plasticity as a useful neurophysiological biomarker for Alzheimer’s disease pathology

ObjectiveAmyloid-beta (Aβ) and tau accumulations impair long-term potentiation (LTP) induction in animal hippocampi. We investigated relationships between motor-cortical plasticity and biomarkers for Alzheimer’s disease (AD) diagnosis in subjects with cognitive decline. MethodsTwenty-six consecutive subjects who complained of memory problems participated in this study. We applied transcranial quadripuse stimulation with an interstimulus interval of 5 ms (QPS5) to induce LTP-like plasticity. Motor-evoked potentials were recorded from the right first-dorsal interosseous muscle before and after QPS5. Cognitive functions, Aβ42 and tau levels in the cerebrospinal fluid (CSF) were measured. Amyloid positron-emission tomography (PET) with11C-Pittsburg compound-B was also conducted. We studied correlations of QPS5-induced plasticity with cognitive functions or AD-related biomarkers. ResultsQPS5-induced LTP-like plasticity positively correlated with cognitive scores. The degree of LTP-like plasticity negatively correlated with levels of CSF-tau, and the amount of amyloid-PET accumulation at the precuneus, and correlated with the CSF-Aβ42 level positively. In the amyloid-PET positive subjects, non-responder rate of QPS5 was higher than the CSF-tau positive rate. ConclusionsFindings suggest that QPS5-induced LTP-like plasticity is a functional biomarker of AD. QPS5 could detect abnormality at earlier stages than CSF-tau in the amyloid-PET positive subjects. SignificanceAssessing motor-cortical plasticity could be a useful neurophysiological biomarker for AD pathology.

The Influence of Body Posture on the Mirror Neuron System

Though the mirror neuron system (MNS) is studied in the scientific community, the influence of the body posture on the functioning of the MNS, as well as on the excitatory and inhibitory system of the brain, has not been revealed yet. In our study, we investigated the functioning of the MNS in case of head rotation. Participants underwent a session of the mirror task, while they were observing movements of the little finger and the index finger of a static hand in three head positions (left, straight and right), combined with transcranial magnetic stimulation (TMS) that was applied at various time intervals. Results showed significant interactions between the movement type and the targeted muscle (F[1,113–16,688] = 9.47, MSE = 56296.14, p = .006, partial η2 = .39). This indicates a robust increase in the activation of the First Dorsal Interosseous (FDI) muscle during the index finger movement (p = .01) and the neutral movement (p .001) observation compared to the little finger movement. Conversely, a significant inhibition of the Abductor Digiti Minimi (ADM) muscle activity was observed during the index finger movement compared to neutral (p = .026). A reversed effect emerged during the little finger movement observation, with higher activation for the ADM muscle and inhibition of the FDI muscle (p = .037). These findings suggest an intricate interplay between MNS activation and muscle activation, indicating an increase in muscle activity corresponding to the observed finger movement and simultaneous inhibition of the muscle not involved in the observed movement.

Cerebellar repetitive transcranial magnetic stimulation has no effect on contraction-induced facilitation of corticospinal excitability.

This study aimed to investigate whether the cerebellum contributes to contraction-induced facilitation (CIF) of contralateral corticospinal excitability. To this end, repetitive cerebellar transcranial magnetic stimulation (TMS) was used to test whether it modulates CIF. Overall, 20 healthy young individuals participated in the study. Single-pulse TMS was applied to the left primary motor cortex to induce motor-evoked potentials (MEP) on electromyography of the right first dorsal interosseous (FDI) muscle to test corticospinal excitability. This measurement was conducted during contraction (10% maximum voluntary contraction [MVC]) and rest (0% MVC) of the FDI muscle. CIF, cerebellar brain inhibition (CBI), cortical silent period (cSP), and resting motor threshold (rMT) were measured before and after low-frequency repetitive TMS (crTMS) of the right cerebellum to downregulate cerebellar output. The CIF (contraction/rest of the MEP), CBI (conditioned/unconditioned MEP) during contraction, cSP, and rMT were not affected by crTMS. At rest, CBI was decreased. These findings indicated that the primary motor cortex function for the increase in corticospinal excitability was not affected by crTMS. This study contributes to our understanding of the role of the cerebellum in motor control. Additionally, it may inform decision-making for the site of cerebellar ataxia treatment using non-invasive brain stimulation.

Comparing the remote effects of dry needling and ischemic pressure on pain intensity and threshold of the myofascial trigger points in women: A Single Blinded Randomized Clinical Trial

ObjectiveThe current study aimed to investigate the remote effects of upper trapezius (UT) Dry needling (DN) and ischemic pressure (IP) on the pain intensity and threshold of the MTrPs in the extensor carpi radialis longus (ECRL) and the first dorsal interosseous (FDI) muscles. MethodsTwenty-eight subjects were allocated into two groups in a randomized clinical trial study undergoing DN and IP interventions on the MTrPs of the UT muscle for 3 sessions. Pressure pain intensity was assessed by visual analog scale (VAS) and pressure pain threshold (PPT) before and after interventions. Upper limb functions were evaluated by the disabilities of the arm, shoulder, and hand (DASH) questionnaire. ResultsThere were significant interactions between muscle, group, and time for PPT, muscle and group, group and time, and muscle and time for VAS (P < 0.05). In DN group, PPTs and VAS of the ECRL and FDI were changed after treatment in all sessions (P < 0.05). In ECRL and FDI muscles, the DN was more effective than IP (P < 0.05). Comparing the pain intensity and threshold of the ECRL, FDI, and UT muscles it was revealed that the improvement in symptoms of the ECRL muscle was the most in the DN group (P < 0.05). There was a significant interaction between group and time for DASH (P < 0.05). In both groups, the DASH score was reduced (P < 0.001). ConclusionsUT muscle DN demonstrated significantly better remote effects in alleviating symptoms of the ipsilateral distal muscles than IP. Both interventions were effective in improving the upper limb function in myofascial pain syndrome patients. Implications for practice•This study evaluated the remote effects of most common treatments on myofascial trigger points.•Dry needling showed therapeutic effects on pain alleviation in terms of both immediate and short term in the extensor carpi radialis longus muscle.•First dorsal interosseous pain threshold and intensity improved following dry needling of the upper trapezius while it is not connected to the upper trapezius muscle myofascially.

The intensity of transspinal direct current stimulation affects the excitability of the corticospinal system

BACKGROUND: Transspinal direct current stimulation (tsDCS) affects the corticospinal system, one of the central human systems associated with controlling precise voluntary movements. Stimulation effects are very sensitive to montage and protocols of applied stimulation because they can involve different neuronal mechanisms. AIM: This study aimed to estimate the effects of parameters of anodal tsDCS applied at the level of the spinal cord (C7–Th1 segments) with cervical enlargement to determine the excitability of the corticospinal system and the correction of motor skills in healthy people. METHODS: The study involved 81 healthy adults aged 21.19±3.20 years. The effect of tsDCS was assessed using motor-evoked potentials from the first dorsal interosseous (FDI) muscle by transcranial magnetic stimulation in the primary motor cortex before stimulation, immediately after stimulation, and after 15 min. RESULTS: The application of 11-min anodal tsDCS at the C7–Th1 level with a current of 1.5 mA affects the FDI muscle, initially reducing the amplitude of transcranial magnetic stimulation induced motor-evoked potentials immediately after stimulation. The amplitude of the motor-evoked potentials increases after 15 min of stimulation. tsDCS with an intensity of 2.5 mA does not affect the change in the amplitude of motor-evoked potentials. Similarly, no difference was found in the effect of 1.5 mA stimulation on the correction of motor skills in healthy adults at the nine-hole peg test and the serial reaction time task as with 2.5 mA. CONCLUSION: This study adds information about the optimally appropriate current intensities of stimulation to induce corticospinal system excitability and the ability of tsDCS to influence motor skills in healthy adults.

Sensitivity Analysis of CMAP Scan Step Index to Different Stimulation Parameters and Examination of Muscles Affected by Spinal Cord Injury.

Step index (STEPIX) is a recently developed compound muscle action potential (CMAP) scan method for evaluating motor unit loss and remodeling changes. This study investigates the influence of different stimulation parameters during CMAP scan on STEPIX and its examination of muscles affected by spinal cord injury (SCI). CMAP scan of the first dorsal interosseous (FDI) muscle was performed using different stimulus pulse widths (0.1 ms, 0.2 ms) and different numbers of stimuli (500, 1000) in 12 neurologically intact subjects. STEPIX was derived from each CMAP scan of all subjects. A significantly higher STEPIX was obtained using 1000 stimuli than 500 stimuli, while no significant difference in STEPIX was observed using 0.1 and 0.2 ms stimulus pulse widths. STEPIX was further applied to process CMAP scans of the FDI muscle from 13 tetraplegia and 13 healthy control subjects using the same stimulation parameter setting (0.1 ms, 500 stimuli), along with other methods including MScanFit motor unit number estimation (MUNE) and D50. STEPIX was significantly lower for the SCI subjects compared with the healthy control subjects. STEPIX was significantly correlated with MscanFit MUNE and D50, but had a smaller relative width of the overlapping zone (WOZ%) between tetraplegic and healthy control groups compared with MScanFit MUNE and D50. The findings of the study highlight the importance of maintaining a consistent stimulation parameter setting in CMAP scan studies and confirm the usefulness of STEPIX as a convenient CMAP scan parameter for examination of motor unit number changes.

First dorsal interosseous muscle reconstruction: a systematic review of its attachments.

The first dorsal interosseous (FDI) muscle, when impaired due to traumatic injuries or degenerative conditions, can be reanimated in various ways to restore pinch grip. These reconstructive techniques are planned based on a precise anatomical understanding of the FDI muscle. However, a review of the existing literature has brought to light controversy regarding its insertions. A systematic review of these descriptions is presented to appreciate these variations. An electronic database search without exclusion by publication year and language was performed according to the Checklist for Anatomical Reviews and Meta-Analyses (CARMA) guidelines, using the PubMed, Scopus, Web of Science and Embase databases. An assessment of the methodological quality was performed. Thirteen studies were included in this article. There is general agreement that the FDI muscle contains two bellies and a bony insertion into the index finger proximal phalanx base. However, due to wide anatomic variation, differences were reported on whether there is a soft tissue insertion. When this was found, the included studies differed on how commonly this occurs (between 1.4% and 78%), where it inserts. Other sites of distal insertions reported include the metacarpophalangeal capsule, the interosseous hood and an assemblage nucleus on the volar plate. Our systematic review, focusing on the insertion of the FDI muscle, summarizes the existing knowledge on its anatomy and variations, thereby facilitating better understanding of its function and surgical planning for reconstruction.

Neurophysiological grading tool of ulnar nerve entrapment across the elbow

Ulnar nerve entrapment across the elbow (UNEAE) is the second most common entrapment of the hand after carpal tunnel syndrome. There are few grades available for UNEAE with their limitations. The aim of this research is to establish, using the best available evidence, a clinically appropriate revision of the current ulnar nerve conduction grading tool and to evaluate its effectiveness in terms of acceptability, without any invasive tests. To compare the recording from the first dorsal interosseous (FDI) muscles with the abductor digiti minimi (ADM) muscle to see which muscle is more sensitive and shows early changes in ulnar nerve entrapment. The revised scale is designed from a clinical physiologist’s perspective and is based on the numerical values of nerve conduction findings. It could also assist surgeons to use this as a tool for interventional prediction. The proposed revised grading system is based on more nuanced, descriptive categories, ranging from “normal, “early, “mild, “moderate, “severe,” and “complete” absence. An additional category of clinical grading is therefore proposed. Method: Data was collected based on the extensive and detailed grading system previously described by Padua. The tests were performed by a qualified clinical physiologist (neurophysiology) using a Keypoint 9033A07 machine, used in line with the departmental protocol (peripheral protocol 1, 2015). The Association of Neurophysiological Scientists (ANS) and British Society of Clinical Neurophysiology (BSCN) (2014) guidelines and minimum standards for the practice of clinical neurophysiology in the United Kingdom were followed. All data was recorded numerically to ensure methodological reliability. Result: The data was collected over the course of one year (2017). A total of 190 patients were involved in this study. A collection of 278 consecutive symptomatic hands was tested for conduction block across the elbow while recording from the first dorsal interosseous FDI muscles. Out of the 278 samples, 201 hands were graded as having normal conduction velocity: 9 hands showed early changes, 51 hands showed mild changes, 14 hands showed moderate changes, 2 hands showed severe changes, and 1 hand showed complete absence or no response from the wrist and across the elbow. Additional studies were carried out from the abductor digiti minimi (ADM) muscles for those patients who showed conduction block across the elbow while recording from the FDI muscles. Only 57 patients underwent a nerve conduction study for ADM. 77 symptomatic hands were tested for conduction block in the ADM muscle. 18 hands were graded as normal; 48 hands showed mild changes; 10 hands showed moderate changes; and 1 hand showed complete absence or no response from the wrist and across the elbow. Out of 278 hands, 266 hands were graded as having normal amplitude across the elbow while recording from FDI muscles; 7 hands showed early changes in amplitude; 1 hand showed moderate amplitude change; 4 hands showed severe amplitude changes; and 1 hand showed complete absence or no response from the wrist and across the elbow. Out of 77 hands, 73 hands showed normal amplitude across the elbow while recording from ADM muscles; 2 hands showed mild changes; 1 hand showed a moderate change; and 1 hand showed complete absence or no response from the wrist and across the elbow. Conclusion: Finding show that FDI is more sensitive in comparison to ADM to record early changes in ulnar nerve entrapment across the elbow. In addition, it shows that a drop in amplitude is not as significant when compared to a conduction block across the elbow.

Increased paired stimuli enhance corticospinal-motoneuronal plasticity in humans with spinal cord injury.

Paired corticospinal-motoneuronal stimulation (PCMS) has been used to enhance corticospinal excitability and functional outcomes in humans with spinal cord injury (SCI). Here, we examined the effect of increasing the number of paired pulses on PCMS-induced plasticity. During PCMS, corticospinal volleys evoked by transcranial magnetic stimulation (TMS) over the hand motor cortex were timed to arrive at corticospinal-motoneuronal synapses of the first dorsal interosseous (FDI) muscle 1-2 ms before the arrival of antidromic potentials elicited in motoneurons by electrical stimulation of the ulnar nerve. We tested motor-evoked potentials (MEPs) elicited by TMS over the hand motor cortex and electrical stimulation at the cervicomedullary junction (CMEPs) in the FDI muscle before and after 180 paired pulses (PCMS-180) followed up by another 180 paired pulses (PCMS-360) in humans with and without chronic incomplete cervical SCI. The nine-hole-peg-test (9HPT) was measured before and after PCMS paired pulses in individuals with SCI. We found that the size of MEPs and CMEPs increased after PCMS-180 in both groups compared with baseline and further increased after PCMS-360 in participants with SCI, suggesting a spinal origin for these effects. Notably, in people with SCI, the time to complete the 9HPT decreased after PCMS-180 and further decreased after PCMS-360 compared with baseline but not when the 9HPT was repeated overtime. Our findings demonstrate that increasing the number of PCMS paired pulses potentiates corticospinal excitability and voluntary motor output after SCI, likely through spinal plasticity. This proof-of-principle study suggests that increasing the PCMS dose represents a strategy to boost voluntary motor output after SCI.NEW & NOTEWORTHY Paired corticospinal-motoneuronal stimulation (PCMS) has been used to enhance corticospinal excitability and functional outcomes in humans with spinal cord injury (SCI). Here, we demonstrate that 360 paired pulses resulted in larger increases in motor-evoked potential size in a hand muscle and in a better ability to complete the nine-hold-peg-test compared with 180 paired pulses in people with SCI. This proof-of-principle study suggests that increasing the PCMS dose represents a strategy to boost motor output after SCI.

First dorsal interosseous muscle transfer to restore opposition of the new thumb after index pollicization: anatomical description of an original technique and case report

Index pollicization in severe thumb hypoplasia or aplasia in children or for the reconstruction of a mutilated thumb in adults is a rare and technically demanding procedure. Weakness of the new thumb is routinely reported after index pollicization. An inappropriate position of the first dorsal interosseous muscle (FDIM) can partly explain this strength deficit. Here, we report an original anatomical study on FDIM transfer for reanimation of the new thumb’s opposition function and its clinical application. An anatomical study was carried out on three upper limbs from fresh, non-embalmed adult cadavers. We demonstrated the feasibility of an FDIM transfer pedicled on the proper FDIM artery and the deep branch of the ulnar nerve. The proximal FDIM insertions were sutured to the lateral border of the flexor retinaculum to recreate the superficial thenar musculature. This procedure was performed on a 52-year-old man who was referred to us with swelling on his hand. We discovered a myxoid inflammatory fibroblastic sarcoma of the thumb that required proximal thumb amputation while preserving the base of the first metacarpal. To our knowledge, this is the first description of FDIM pedicled flap transfer during an index pollicization procedure among an adult population. However, in severe thumb hypoplasia or aplasia cases, this procedure is limited by the size and anatomical variations of the neurovascular structures among a population affected by radial longitudinal deficiency.

The Sensitivity and Specificity of Split-Hand Index Using Muscle Sonography.

The split-hand index (SHI) (first dorsal interosseous (FDI) × abductor pollicis brevis (APB)/abductor digiti minimi muscle (ADM)) has been suggested as a useful measure for amyotrophic lateral sclerosis (ALS) diagnosis, using electrophysiological and sonographic indices. In the present study, we aimed to explore the specificity of SHI derived by muscle ultrasound (MUS) for the diagnosis of ALS and spinal muscular atrophy (SMA). Healthy controls (n = 65) were prospectively recruited at the Prosserman Family Neuromuscular clinic at Toronto General Hospital, from October to December 2018. In addition, 181 patients with ALS (n = 91), SMA (n = 33), polyneuropathy (n = 35), and myopathy (n = 22) were prospectively recruited at the neuromuscular clinic at Tel Aviv Sourasky Medical Center, from December 2018 to December 2020. All subjects underwent quantitative sonographic evaluation of muscle thickness, including the right APB, FDI, and ADM muscles. Area under curve (AUC), sensitivity, and specificity were determined for differentiating between groups. Although SHI showed good to excellent accuracy for differentiating each patient subgroup from controls (AUC 0.83-0.92), poorer diagnostic accuracy was shown for differentiating between different patient subgroups (AUC 0.54-0.74). Sonographic SHI is useful for differentiating patients from healthy controls, but might be not specific for motor neuron disease.

Effect of repeated eccentric exercise on muscle damage markers and motor unit control strategies in arm and hand muscle

To examine the contralateral repeated bout effect (CL-RBE) on muscle damage markers and motor unit (MU) control strategies, seventeen healthy adults performed two bouts of 60 eccentric contractions with elbow flexor (EF group; n ​= ​9) or index finger abductor (IA group; n ​= ​8) muscles, separated by 1 week. All participants randomly performed eccentric exercise on either the right or left arm or hand muscles, and muscle damage markers and submaximal trapezoid contraction tests were conducted pre, post, 1- and 2-day post eccentric protocol. One week after the first bout, the same exercise protocol and measurements were performed on the contralateral muscles. Surface electromyographic (EMG) signals were collected from biceps brachii (BB) or first dorsal interosseous (FDI) during maximal and submaximal tests. The linear regression analyses were used to examine MU recruitment threshold versus mean firing rate and recruitment threshold versus derecruitment threshold relationships. EMG amplitude from BB (bout 1 vs. bout 2 ​= ​65.71% ​± ​22.92% vs. 43.05% ​± ​18.97%, p ​= ​0.015, d ​= ​1.077) and the y-intercept (group merged) from the MU recruitment threshold versus derecruitment threshold relationship (bout 1 vs. bout 2 ​= ​−7.10 ​± ​14.20 vs. 0.73 ​± ​16.24, p ​= ​0.029, d ​= ​0.513) at 50% MVIC were significantly different between two bouts. However, other muscle damage markers did not show any CL-RBE in both muscle groups. Therefore, despite changes in muscle excitation and MU firing behavior, our results do not support the existence of CL-RBE on BB and FDI muscles.

Intensity dependency of peripheral nerve stimulation in spinal LTP induced by paired associative corticospinal-motoneuronal stimulation (PCMS).

Paired associative corticospinal-motoneuronal stimulation (PCMS) induces plasticity at synapses between corticospinal tracts (CSTs) and spinal motoneurons (SMs). We investigated the effects of peripheral nerve electrical stimulation (PNS) intensity on PCMS-induced plasticity. PCMS consisted of 180 paired stimuli of transcranial magnetic stimulation (TMS) over the left primary motor cortex with PNS on the right ulnar nerve at the wrist. We compared effects induced by different PNS intensities: supramaximal, twice and three times sensory threshold intensities. For evaluating efficacy of the synapse between CSTs and SMs, single-pulse TMS was delivered at cervicomedullary junction level, and cervicomedullary motor-evoked potentials (CMEPs) were recorded from the right first-dorsal interosseous muscle before and after PCMS. PCMS with the supramaximal PNS intensity increased CMEP amplitude. The facilitatory effect of PCMS with the supramaximal PNS was larger than those of PCMS with weaker PNS intensities. Sham TMS with the supramaximal PNS showed no CMEP changes after the intervention. PNS intensity of PCMS influences the magnitude of synaptic plasticity induction between the CSTs and SMs at the spinal level, and the supramaximal intensity is the best for induction of long-term potentiation-like effects. The PNS intensity may influence the number of activated SMs by axonal backpropagating pulses with PNS which must overlap with descending volleys induced by TMS.

The Effect of Local Cooling at the Elbow on Nerve Conduction Velocity and Motor Unit Behaviour: An Exploration of a Novel Neurological Assessment.

Background: This study aimed to determine the effects of a standard therapeutic cooling protocol using crushed ice on the elbow to explore if changes in the motor unit (MU) firing rates in the first dorsal interosseous (FDI) muscle are comparable to known changes in sensory and motor nerve conduction velocity (NCV) due to a regional temperature drop around a peripheral nerve. Methods: Twelve healthy individuals were assessed before cooling, immediately after cooling, and 15 min of rewarming. Assessments included two standard non-invasive nerve conduction velocity tests and a non-invasive investigation of the MU firing rates using surface electromyography decomposition (dEMG). Results: Repeated ANOVAs showed significant differences in the MU firing rates and NCV between time points (p = 0.01 and p < 0.001). All measures showed significant differences between pre and post cooling and between pre-cooling and 15 min of passive re-warming, however, no changes were seen between post cooling and rewarming except in the sensory NCV, which increased but did not return to the pre-cooled state. Conclusions: This current study showed a significant, temporary, and reversible reduction in ulnar NCV across the elbow in healthy subjects, which was associated with a significant decrease in mean MU firing rates in the FDI muscle.

WS3.4. Electrodiagnostic Approach to Motor Neuron Disease: Split Hand in ALS

Amyotrophic lateral sclerosis (ALS) is characterized by involvement of both upper and lower motor neurons. Electrophysiologic approach includes EMG (denervation potentials and fasciculation potentials) and nerve conduction studies (NCS; low CMAP, decreased motor unit number, and axonal hyperexcitability on nerve excitability testing) for lower motor neuron involvement, and transcranial magnetic stimulation with threshold tracking (decreased short- latency intracortical inhibition) for upper motoneuronal hyperexcitability. Of these, routine NCS can detect the “split hand” pattern, which is a very important indicator for diagnosis, because this symptom has been recognized as being specific to ALS; the thenar and first dorsal interosseous (FDI) muscles are preferentially affected. In contrast, the hypothenar muscle (abductor digiti minimi, ADM) is relatively preserved. FDI and ADM muscles are innervated by the same C8/Th1 spinal segments and the same ulnar nerve. The split hand indicates a potentially specific pathological mechanism, suggesting hyperexcitability of both upper and lower motor neuron/axons. Along with this symptom, wide-spread fasciculations are prominent clinical features in patients with ALS, specifically seen in ALS among disorders with neurogenic muscle atrophy. Fasciculations frequently arise from the motor nerve terminals, and the hyperexcitability of motor axons appears to constitute the pathophysiology of the disease. Neurophysiologic investigations of the upper and lower motor neurons/axons have shown increased excitability. The altered excitability is supposed to relate to motor neuron death.

Experimental Hand and Knee Pain Cause Differential Effects on Corticomotor Excitability

Acute pain elicits a well-known inhibitory effect on upper limb corticomotor excitability, whereas the temporal effects of lower-limb experimental pain and pain in a remote limb are less clear. The aim of this study was to compare the temporal corticomotor excitability changes in the upper and lower limbs in response to acute upper and lower limb pain. In a cross-over design, 13 participants (age 29 ± 9 years; 12 male) attended 2 sessions where experimental pain was induced by injecting hypertonic saline into either the first dorsal interosseous (FDI) muscle or infrapatellar fat pad at the knee, inducing a short-lasting pain experience scored on a numerical rating scale (NRS). Motor evoked potentials (MEPs) in response to transcranial magnetic stimulation were recorded in the FDI and vastus lateralis (VL) muscles before, during, and following pain. Hand and knee pain NRS scores were not significantly different. Hand pain elicited a short duration inhibition of the FDI MEPs (P < .0001) together with a facilitation of VL MEPs (P = .001) that outlasted the duration of pain. Knee pain elicited a short-duration facilitation of VL MEPs (P = .003) with no significant effect in the FDI MEPs (P = .46). The findings indicate a limb-specific corticomotor response to experimental pain that may be related to limb function. PerspectiveThese data demonstrate the impact of acute, experimental pain on corticomotor excitability in the upper and lower limbs. This facilitates our understanding of the effect of pain on motor control of both local and distant muscles.

CMAP Scan Examination of the First Dorsal Interosseous Muscle After Spinal Cord Injury.

The study assessed motor unit loss in muscles paralyzed by spinal cord injury (SCI) using a novel compound muscle action potential (CMAP) scan examination. The CMAP scan of the first dorsal interosseous (FDI) muscle was applied in tetraplegia (n = 13) and neurologically intact (n=13) subjects. MScanFit was used for estimating motor unit numbers in each subject. The D50 value of the CMAP scan was also calculated. We observed a significant decrease in both CMAP amplitude and motor unit number estimation (MUNE) in paralyzed FDI muscles, as compared with neurologically intact muscles. Across all subjects, the CMAP (negative peak) amplitude was 8.01 ± 3.97 mV for the paralyzed muscles and 16.75 ± 3.55 mV for the neurologically intact muscles (p < 0.001). The CMAP scan resulted in a MUNE of 59 ± 37 for the paralyzed muscles, much lower than 108 ± 21 for the neurologically intact muscles (p < 0.001). No significant difference in D50 was observed between the two groups (p= 0.2). For the SCI subjects, there was no significant correlation between MUNE and CMAP amplitude, or any of the clinical assessments including pinch force, grip force, the Graded Redefined Assessment of Strength, Sensibility and Prehension (GRASSP) score, and SCI duration (p > 0.05). The findings provide an evidence of motor unit loss in the FDI muscles of individuals with tetraplegia, which may contribute to weakness and other hand function deterioration. The CMAP scan offers several practical benefits compared with the traditional MUNE techniques because it is noninvasive, automated and can be performed within several minutes.

On the Reuse of Motor Unit Filters in High Density Surface Electromyograms Recorded at Different Contraction Levels

We analyzed the efficiency of Motor Unit (MU) tracking across different experimentally recorded contraction levels of Biceps Brachii (BB), Tibialis Anterior (TA), First Dorsal Interosseous (FDI) and Abductor Digiti Minimi (ADM) muscles and in simulated conditions. We used the Convolution Kernel Compensation (CKC) algorithm to estimate the MU filters from high-density electromyograms (HDEMGs) at contraction levels ranging from 5 % to 70 % of Maximum Voluntary Contraction (MVC), and applied these MU filters to all the recorded contractions levels of the same muscle. For each MU filter estimation-application pair we assessed the number of identified MUs, Pulse-to-Noise Ratio (PNR), Mean Discharge Rate (MDR) and MUAP peak-to-peak (P2P) amplitude, normalized by HDEMG P2P amplitude. In simulated conditions, we also calculated the Precision ( $Pr$ ) and Sensitivity ( $Se$ ) of MU firing identification. We also reported the number of jointly identified MUs for all possible contraction level pairs. The results in simulated conditions confirmed the efficiency of MU filter transfer from low to high contraction levels. The large majority of MUs identified at lower contraction levels were tracked successfully at higher contraction levels, though many of them were not directly identified at higher contraction levels. Sensitivities of identified MU firings were above 97 %, decreasing only by about 1 % when transferring the MU filters from low to high contraction levels. In the experimental conditions the efficiency of the MU tracking depended significantly on the investigated muscle. The highest efficiency was demonstrated in the FDI muscle, where about 90 % and 70 % of MUs identified at the contraction level of MU filter estimation were also tracked at 10 % and 20 % higher contraction level, respectively. These figures decreased to 47 % and 20 % of MUs in TA, and to 21 % and 18 % of MUs in the BB muscle. The observed differences between the MU filter transfer efficiencies are likely caused by the differences in the size and anatomy of the investigated muscles.